Fiber-to-the-home (FTTH) systems support a variety of communication devices and services. Whilst multiple architectures have been proposed and assessed the dominant approach today is based upon that of a Passive Optical Network (PON) that provides for a distribution of services to customers over a reduced physical infra-structure. As the services provided evolve then the industry standards cover a series of steps from Broadband-PON (B-PON) through Ethernet-PON (E-PON), to Gigabit-PON (G-PON) and ultimately to Wavelength Division Multiplexed PON (WDM-PON).
Common to all of these PON architectures and FTTH systems is the requirement for a subscriber interface that provides and receives optical signals via a single optical waveguide. The use of bi-directional transmission over the single optical waveguide reduces the infrastructure requirements and further lowers cost. From the emergent industry standards the FTTH system is generally based upon the use of optical signals at three wavelengths (at approximately 1310 nm/1490 nm/1550 nm) and a component that provides the subscriber interface at the set-top box or residence interface is called a triplexer. This optical triplexer transmits one optical signal upstream (at approximately 1310 nm) whilst it receives two optical downstream signals at approximately 1490 nm and 1550 nm wavelengths. These signals are separated by wavelength allowing a first wavelength, typically 1550 nm, to be dedicated to video signals and the second wavelength, typically 1490 nm, to be used for voice and data signals.
At present such an optical triplexer would be manufactured by combining a variety of discrete components into an assembly. These components include: a 1310 nm laser source with a photodiode for providing a feedback signal, a first wavelength division multiplexer (WDM) for segregating the 1310 nm signals from the 1490 nm and 1550 nm signals, a second WDM for separating the 1490 nm signals from the 1550 nm signals and a set of photodetectors for sensing the 1490 nm and 1550 nm signals. Said laser and photodetectors being previously assembled and hermetically sealed components in their own rights. As such these triplexers are expensive due to using multiple sub-components which are highly manufactured entities themselves, alongside the high labor elements of combining these components both physically but also performing the final alignment and adjustment. As such these triplexers are sufficiently expensive that system carriers do not commercially support their use in single family dwellings thereby limiting the penetration of very high speed services to the general population.
Instead it would be highly desirable to provide all the necessary components in a single waveguide substrate, or chip. Unfortunately, the present state of optical technology suggests that the optical triplexer components be integrated monolithically onto an indium phosphide based waveguide component and even then these components are not easily combined. Specifically, any common waveguide portion of the device is intended to support 1310 nm, 1490 nm and 1550 nm optical signals simultaneously. Although passive optical waveguides will support these widely separated wavelengths over reasonable distances it is very difficult to produce an active waveguide substrate with an optical waveguide that supports optical signals at all three wavelengths with good performance. Consequently, the integrated optical triplexers feature common waveguides that are intended to propagate optical signals at the longest supported wavelength, in this case 1550 nm. Unfortunately, this results in substantial attenuation of any optical signals provided by the 1310 nm wavelength source. It would be beneficial to provide an optical triplexer that does not substantially attenuate 1310 nm optical signals.
As such searches for prior art of integrated optical triplexers result in an absence of material. Current research and identified prior art relates to the integration of solely the WDM elements onto a planar waveguide substrate such as silica-on-silicon and the subsequent hybrid integration of these along with the semiconductor laser and photodetectors.